The present invention concerns an electromagnetic noise measurement apparatus for measuring electromagnetic noise generated from a concerned electromagnetic noise measurement body under operation, for example, a printed circuit board.
2. Description of the Related Art
In electrical devices, as represented by computers having a clock frequency exceeding 100 MHz, digitalization of such electrical devices and high speed operation thereof is progressing. Because high frequency noise is generated, including successive even and odd numbers from binary digital signals therefrom, an electromagnetic noise measurement apparatus covering the GHz band has been desired.
As types of electromagnetic noise measurement apparatuses for measuring electromagnetic noise, there are for example, the disclosures of Japanese Patent publication No. 5-67184, Japanese Laid-Open Patent publication No. 6-58969 and Japanese Laid-Open Patent publication No. 6-58970. In Japanese Patent publication No. 5-67184, an antenna made up of a wire which generates an electrical output corresponding to electromagnetic radiation from an electromagnetic radiating body is disposed in proximity to the electromagnetic radiating body, the output from the antenna is sequentially selected by a diode matrix and transmitted to a measurement receiving device, the electromagnetic radiation level is analyzed by the measurement signal receiving device, and a mapping showing electromagnetic radiation levels at positions confronting the antenna in the vicinity of the electromagnetic radiating body is generated from the analyzed measured electromagnetic radiation levels.
On the other hand, in the disclosures of Japanese Laid-Open Patent publication Nos. 6-58969 and 6-58970, a near magnetic field probe is caused to confront a printed circuit board which is installed in an electrical device emitting much unnecessary radiation, the near magnetic field probe is moved in X-Y-Z axial directions with respect to the printed circuit board, and electromagnetic noise is measured based on an output from the near magnetic field probe.
Further, in the disclosure of Japanese Laid-Open Patent publication No. 6-58970, a printed circuit board disposed in an electrical device is placed on an antenna for measuring interference, wherein measurements including electromagnetic noise of surfaces of the printed circuit board are made.
On the other hand, as an interference measuring antenna for detecting a magnetic field of unnecessary radiation, there is the disclosure of Japanese Laid-Open Patent publication No. 6-58971. This interference measurement antenna is made up of a multi-turn coil which is connected in series to a coil constructed as a pattern in the same position atop a multi-layer printed circuit board, wherein a surface-installed condenser is made internal with the printed circuit board, the multi-turn coil and condenser are connected, and an LC resonant circuit is arranged as a matrix on the printed circuit board.
Notwithstanding, apart from the problem that in the measurement of electromagnetic noise by the electromagnetic noise measurement apparatuses of the above-mentioned prior art, measurement of electromagnetic noise covering the GHz band is problematic, there is also the problem that an antenna must be arranged at a predetermined interval in a plane which is wider than the area of the concerned electromagnetic noise measurement body under operation.
Furthermore, because the antenna is arranged in a plane, a distance-based measurement interval is fixed by the distance from the antenna, and measurement resolution cannot be made small.
Still further, the antenna cannot capture, as a near magnetic field, a current which flows through an electronic circuit.
Further, in the disclosures of Laid-Open Patent publication Nos. 6-58969 and 6-58970, because measurements are made while driving the near magnetic field probe in X-Y-Z axial directions, in spite of the fact that the time of electrical measurement is shortened, time is required for mechanical movement of the near magnetic field probe, and there is the problem that high speed measurement is difficult.
Further, in the measurement of electromagnetic noise by the electromagnetic noise measurement apparatuses of the above-mentioned prior art, because a drive motor for moving the near magnetic field probe is always operated, elimination of electromagnetic noise due to the motor becomes necessary and the motor must be distanced from the near magnetic field probe, also resulting in the problem that the apparatus becomes increased in complexity.
Further, when using the interference measurement antenna of the above-mentioned prior art, there is the problem that only electromagnetic noise of a narrow frequency band, in which sensitivity is improved by constructing a resonant circuit, can be measured. For widening the frequency band, it becomes necessary to raise the resonant frequency, however when made small in size with a few MHz frequency band, there is the problem that the sensitivity thereof is diminished.
Furthermore, when using the interference measuring antenna of the above-noted prior art, when the coil number is increased the antenna surface shields the measured electromagnetic noise of concern, and there is also a problem that the direction of the magnetic field components which make up the electromagnetic noise are bent and accurate measurement thereof cannot be conducted.
Moreover, in the electromagnetic noise measurement apparatus of the prior art, apart from electromagnetic noise levels, such apparatuses cannot enable measurement together with measuring the direction of generation of the electromagnetic source.